1. Field of the Invention
The present invention relates to a lifting device, and more particularly to a lifting device for a platform of treadmills.
2. Description of Related Art
A conventional lifting device for a platform of a treadmill in accordance with the prior art shown in FIG. 7 is adapted to be mounted between a stand (6) and a platform (7) of the treadmill. The lifting device comprises two first linkages (81), two second linkages (82) each pivotally connected to a corresponding one of the two first linkages (81) and a telescope shaft (83) for adjusting the working angle of the platform (7) and driving the linkages (81, 82). The stand (6) two opposite lower end each having a projecting rod (61) horizontally extending therefrom. Each first linkage (81) has a first end pivotally connected to a rear portion of the projecting rod (61) and a second pivotally connected to a bottom of the platform (7). Each second linkage (82) has a first end pivotally connected to the second end of each of the two first linkages (81) and a second end connected by an axle (821). The axle (821) includes two opposite ends each having a roller (822) rotatably mounted to the axle (821). The two rollers (822) are moved between the two projecting rods (61) of the stand (6). The telescope shaft (83) is partially received in a motor (831) and  reciprocally telescopically driven by the motor (831). The motor (831) is pivotally connected to the platform (7) and the free end of the telescope shaft (83) is pivotally connected to the axle (821).
With reference to FIGS. 8 and 9, when folding the treadmill, the free end of the telescope shaft (83) is first backwardly moved relative to the motor (831) to make a front end of the platform (7) selectively pivotally to a seat (62) of the treadmill and then the front end of the platform (7) can not be upwardly moved again. Secondary, the telescope shaft (83) extends to make the rollers (822) move toward the first end of the first linkage (81). Lastly, the free end of the telescope shaft (83) is backward moved to continually lift the platform (7) till the platform (7) is perpendicular relative to the supporting surface.
As described above, the telescope shaft (83) is reciprocally moved relative to the motor (831) that may shorten the using life of the telescope shaft (83) and the motor. Furthermore, the platform (7) cannot be lifted when the free end of the telescope shaft (83) has been moved toward the motor (831) and the platform (7) has a small working angle relative to the supporting surface.
The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional lifting device for a platform of a treadmill.